1. Field of the Invention
The present invention relates to a starter to be employed for the start-up of an internal combustion engine by means of an electric motor, and in particular, to a starter provided with an electric motor which is capable of smoothly and reliably starting the internal combustion engine even though the electric motor employed therein is relatively small in size and output.
2. Description of the Related Art
A D.C. motor type starter which is provided with an electric motor for starting an internal combustion engine such as an small air-cooled two-stroke internal combustion engine which is designed to be mounted on a portable power working machine such as a brush cutter is generally constructed, as described in Japanese Utility Model Publication H6-19828, in such a manner that the driving force of an electric motor is directly transmitted via a speed reduction gear mechanism to the crankshaft of the internal combustion engine.
However, since the conventional D.C. motor type starter is designed such that the driving force of the electric motor is directly transmitted, as it is, to the crankshaft, it is required to employ an electric motor which is capable of obtaining a sufficient torque or revolving speed which is required for the start-up of the engine, i.e. an electric motor which is relatively large in size as well as in output.
This results in an increase in power consumption by the motor, thereby necessitating the employment of a battery of large capacity, and at the same time, results in an increase in impact to the motor as well as to the power-transmission system of the motor at the moment of starting the engine, thereby necessitating the employment of constituent components having a large mechanical strength and an increased stiffness for the starter. As a result, the total weight of the starter would be caused to increase, simultaneously raising various problems such as the deterioration of durability of the starter and the failure of the starter due to kick-back, etc.
The present invention has been made in view of the aforementioned problems, and therefore, it is an object of the present invention to provide a starter which is capable of smoothly and reliably starting an internal combustion engine even though the electric motor employed is relatively small in size and output, thereby making it possible to minimize the power consumption of the electric motor, to miniaturize the capacity of battery, to reduce the total weight of the starter, to enhance the durability of the starter, and to suppress the generation of failure of the starter.
With a view to attaining the aforementioned object, there is provided, in accordance with the present invention, a starter which fundamentally comprises a buffering/power-accumulating means disposed midway along the power transmission system between a driving member and a driven (idler) member, wherein the buffering/power-accumulating means is enabled, during the driving process by the driving member, to accumulate the power supplied through the driving process while alleviating any shock to the driven member, the accumulated power being subsequently employed to drive the driven member, and wherein the driving member is an electric motor acting as a driving source.
In a preferred embodiment of the present invention, the driven member is provided with a centrifugal clutch which is designed to be disengaged by an effect of the centrifugal force to be generated by the rotation of the driven member, and the driven member is interlocked via the centrifugal clutch with the driving member.
Preferably, the buffering/power-accumulating means is constituted by a spiral spring mechanism. It is also preferable that a speed-reduction mechanism is interposed between the buffering/power-accumulating means and the electric motor.
In another preferred embodiment of the present invention, the spiral spring mechanism comprises a spiral spring case which is disposed close to the electric motor, an actuating pulley which is disposed close to the driven member, and a spiral spring which is interposed between the spiral spring case and the actuating pulley, wherein an outer end of said spiral spring and an inner end of said spiral spring are secured to the spiral spring case and to the actuating pulley, respectively.
Preferably, the speed-reduction mechanism is constituted by a worm gear device comprising a worm fixed to an output rotation axis of the electric motor, and a worm wheel provided on an outer circumference of the spiral spring case.
Preferably, the spiral spring of the spiral spring mechanism comprises an outer circumferential wound portion where a predetermined number of turns of the outer circumferentially wound portion of the spiral spring are closely contacted with each other under a freely released condition of the spiral spring, and an inner circumferential wound portion which is constituted by at least one turn of the inner circumferentially wound portion of the spiral spring, wherein a clearance is provided between the outer circumferential wound portion and the inner circumferential wound portion. More preferably, the outer circumferential wound portion is constituted by a third turn and the following turns successive to the third turn, and the inner circumferential wound portion is constituted by a first turn and at least a portion of the second turn which is closely contacted with the first turn.
In another preferred embodiment of the present invention, a recoil type driving member is additionally provided close to the driving member in separate from the electric motor, wherein the recoil type driving member comprises a rope reel having a recoil rope wound around the rope reel which is designed to be revolved by pulling the recoil rope, recoil-urging means for urging the rope reel to reversibly revolve to thereby wind up the recoil rope, and a recoil ratchet mechanism for transmitting the rotation of the rope reel to the buffering/power-accumulating means.
In another preferred embodiment of the present invention, the spiral spring mechanism is provided with a one-way clutch which enables the spiral spring case to revolve only unidirectionally.
According to a preferable embodiment of the starter of the present invention having the aforementioned structure, when the internal combustion engine is desired to be started, a starting switch which is separately mounted for the starter should be pushed. As a result, electric current is transmitted for a predetermined period of time (for example, 2 to 3 seconds) from a battery mounted on the engine to the electric motor, thereby enabling the electric motor (the output rotation axis thereof) to rotate for aforementioned predetermined period of time, thus producing a rotational driving force, which is then transmitted, via the spiral spring mechanism constituting the buffering/power-accumulating means and the driven member, to the crankshaft of the internal combustion engine.
In this case, during the first-half driving process by means of the electric motor (until the piston of the internal combustion engine reaches the top dead center of the internal combustion engine), it is possible to derive a buffering effect from the spiral spring mechanism, and at the same time, to accumulate the driving force of the electric motor in a spiral spring mechanism, and during the latter-half driving process, the driving force thus accumulated in the spiral spring mechanism during the first-half driving process is permitted to be combined with the driving force to be actually effected by the electric motor in the latter-half driving process to thereby generate a resultant force, the energy of which being sufficiently large enough to overcome the load of the compression of the engine, thus providing a sufficient energy for starting the internal combustion engine.
Therefore, the internal combustion engine can be smoothly and reliably started an even though the electric motor employed therein is relatively small in size and output, thereby making it possible to minimize the power consumption of the electric motor, to miniaturize the capacity of the battery, to reduce the total weight of the starter, to enhance the durability of the starter, and to suppress the generation of failure of the starter, thus resulting in the improvement of reliability of the starter.